1. Field of the Invention
The present invention relates to boost fuel enrichers used in internal combustion engines equipped with a turbocharger or supercharger. More specifically, the enricher is a device which is usable in carbureted or fuel injected engines with a boost pressure from a turbocharger or supercharger in a blow-through configuration, and which mechanically bypasses more fuel into the air-fuel mixture in order to avoid lean operation.
2. Description of the Related Art
A naturally aspirated internal combustion engine has a volumetric efficiency which is less than 100%. In order to compensate for this problem, many vehicles are equipped with a compressor in the form of a supercharger, in which the compressor is driven either directly by the crankshaft or indirectly by a belt and pulley, or in the form of a turbocharger, in which the compressor is mounted on the same shaft as a turbine driven by the engine""s exhaust gases. The compressor enables a greater density of air to enter the engines cylinders through the intake manifold. The greater density of air in the cylinders permits more complete combustion of the fuel, and a greater mass of gas pushing against the piston, thereby generating more horsepower.
However, one problem associated with supercharged and turbocharged engines is proper adjustment of the air/fuel ratio. In a naturally aspirated engine, a vacuum develops in the intake manifold. When the throttle is opened, air at atmospheric pressure enters the intake manifold to fill the vacuum. The stoichiometric air/fuel ratio is about 14.5:1. The fuel system in a naturally aspirated engine is designed to deliver fuel at a slightly richer ratio under load, about 12:1 to 13:1.
In a supercharged or turbocharged engine, however, the air in the intake manifold is more dense, with pressures often greater than atmospheric. The boost pressure is often defined as the difference between barometric pressure and the pressure in the intake manifold in a supercharged or turbocharged engine. The boost pressure in an automobile designed for ordinary highway use often reaches a pressure of 8-10 psi of boost. Unless a greater quantity of fuel is added to the air/fuel mixture than would be provided in a naturally aspirated engine, the engine may run lean, leading to detonation. In a street machine, detonation can result in damage to the piston, rings, head gasket and other components. In a racing vehicle, which may use aluminum rods and pistons, detonation may result in more sever damage, such as a broken rod and resultant damage to the crankshaft and cylinder walls.
In modern fuel injection engines, this problem is usually addressed by the mass air flow sensor and the electronic engine control, which controls the frequency and duration of the injection pulses according to the quantity of air sensed by the mass air flow sensor. Many engines also have a knock sensor, which may also signal the electronic engine control to increase fuel injection when knock indicative of detonation is sensed. Some fuel injection engines run with little or no modification with a supercharger or turbocharger. Other fuel injection systems require pressure or temperature sensors, or are not programmed or mapped to handle boost pressures above atmospheric pressure, and therefore require chip replacement.
In any event, fuel injection systems frequently respond on the basis of historical data, i.e., the sensors do not respond dynamically to correct the condition sensed, but merely transmit the information to the electronic engine control where the information reported from multiple sensors is analyzed. Further, a response to sensor input may not be formulated immediately. The electronic engine control may have a delay built in to require that the sensor input be repeated over a predetermined time interval to eliminate spurious data before responding. Only then does the controller send an appropriate signal to an actuator or transducer to initiate corrective action, so that in electronic fuel injection systems, there may be a time lag in responding to high boost pressures in the intake manifold.
In carbureted engines, when a supercharger or turbocharger is added, usually a higher octane gasoline is selected to prevent detonation. Other measures include retarding spark ignition, enriching the air/fuel mixture, and cooling the intake charge by water injection or an intercooler. Enriching the fuel mixture usually involves increasing the size of the jets, changing the spring on the main power piston or metering rod, adjusting the idle screw, and other such measures. However, these measures can prove to be quite expensive. It is not unheard of for adjustments to the carburetor and fuel system of a racing car to cost into the five figure range, depending upon the fuel being used. Further, these adjustments cause the engine to run rich whether operated under a light or heavy load. P. Ganahl in Street Supercharging (CarTech, Inc., North Branch, Minn., 1999) describes several such adjustments at pp. 107-118.
Superchargers and turbochargers may be mounted in different configurations. In a xe2x80x9cblow-throughxe2x80x9d configuration, the compressor is upstream from the carburetor, and blows dry air into the carburetor air horn. In a xe2x80x9cdraw-throughxe2x80x9d configuration, the compressor is mounted between the carburetor and the intake manifold, and draws an air-fuel mixture into the manifold. The draw-through configuration presents another problem when used with a carburetor designed for naturally aspirated engines.
As explained by H. MacInnes in Turbochargers, (The Berkley Publishing Group, New York, 1984) at pp. 54-55, a conventional carburetor has a passage extending from below the throttle plate to a power piston or diaphragm controlling a metering rod. When there is vacuum below the throttle plate, the power valve remains closed, but when the throttle plate is opened, the piston or metering rod opens to allow more fuel to enter the air horn. However, when the throttle is then partially released, as under cruise conditions, the power valve closes. In a draw-through configuration, this may result in the power valve closing while the engine is still under boost, resulting in detonation. MacInnes describes modifications to the power valve to avoid this problem, including plugging the passage and providing a separate passage from the power valve to the intake manifold, thereby bypassing the compressor. However, MacInnes points out that this only solves the problem of proper actuation of the power valve, and not adjusting the air/fuel ratio to the increased boost pressure provided by the compressor.
U.S. Pat. No. 4,241,711, issued Dec. 30, 1980 to C. A. Detwiller, describes a fuel control system which adjusts the response of the main metering rod according to the load in a draw-through turbocharger configuration. The system includes a device having a diaphragm which separates a control chamber connected to the intake manifold downstream from the compressor from a regulating chamber connected to the carburetor plenum between the throttle and the compressor. An output tube is connected between the regulating chamber and a vacuum regulator connected to the metering rod. A bias spring is normally set for a low vacuum output. Differential pressure between the control chamber and the regulating chamber controls the metering rod according to the load. However, this only addresses the power valve actuation problem, and does not address the problem of adjusting the air/fuel ratio to the boost pressure.
MacInnes also describes devices which are directed towards adjusting the air/fuel ratio according to the boost pressure in Turbochargers, supra, at pp. 55-58. One such device is a pressure switch connected to the intake manifold which operates a solenoid valve that opens when boost pressure exceeds a specified limit in order to inject additional fuel into the air horn. Another device described is a pressure activate fuel valve with a diaphragm that opens to admit more fuel to the air horn, the fuel valve sensing pressure in the intake manifold downstream from the compressor. MacInnes also describes an arrangement used with a progressive or multibarrel carburetor in which the secondaries open only when the engine is supercharged to enrich the air/fuel mixture.
U.S. Pat. No. 4,558,680, issued Dec. 17, 1985, shows a system for a blow-through turbocharger with an air diaphragm valve having one chamber connected to the intake passage upstream of the carburetor, and the other chamber connected below the throttle valve, the diaphragm operating a needle valve controlling flow between the air cleaner and an air bleed in the carburetor. The conduit between the air diaphragm valve and the intake manifold has a check valve and a bleed to the atmosphere. When the vehicle is under load, the pressure differential between the air horn and the intake manifold opens the needle valve to supply a rich air/fuel mixture. Otherwise the valve is closed to lean the mixture.
U.S. Pat. No. 4,658,798, issued Apr. 21, 1987 to Yogo et al. describes a turbocharger control system adapted for either a blow-through or a draw-through configuration. The Yogo patent describes a device for providing a lean air/fuel mixture when pressure in the intake manifold exceeds a predetermined limit. The device described by Yogo is essentially designed for smoothing transitions when a predetermined pressure limit is exceeded in the intake manifold.
There is a need for a boost fuel enricher which operates mechanically to enrich the air/fuel mixture when an engine is under boost pressure in order to provide a dynamic, continuous adjustment of the air/fuel mixture.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed. Thus a boost fuel enricher solving the aforementioned problems is desired.
The boost fuel enricher is used with internal combustion engines, either carbureted or fuel-injected, that are equipped with compressors, i.e., turbocharged or supercharged, in order to enrich the air/fuel ratio when the engine is under boost. The boost fuel enricher is a diaphragm pressure valve. The diaphragm is subject to atmospheric pressure on one side, and senses inlet air pressure in the air intake passage on the other side. When inlet air pressure exceeds atmospheric pressure, the valve opens to admit additional air-fuel mixture into the air intake passage through a venturi in the air intake passage.
The valve has an adjustable or variable throat to meter the additional fuel within a range required by the desired boost pressure.
In a carbureted engine, the air intake passage includes the carburetor air horn with a venturi defined therein. Boost pressure is assumed to be the air intake pressure communicated through the carburetor bowl vent tube to the carburetor fuel bowl. From the fuel bowl the air intake pressure is communicated to the inlet of the fuel enricher. When air intake pressure exceeds atmospheric pressure, the valve opens and the air-fuel mixture exits the valve through a conduit which discharges into the venturi of the carburetor air horn.
In a fuel injected engine, a venturi, which may be either an auxiliary venturi or a carburetor body modified by plugging the main jets, idle jets, and other orifices, is placed in the air intake passage either between the compressor and the throttle body, or between the intercooler and the throttle body. In the case of an auxiliary venturi, the fuel enricher has its inlet connected to a regulator attached to the fuel pump, the regulator keeping the pressure at about 1 psig above the boost pressure. In the case of the modified carburetor body, the fuel enricher has its inlet connected to the fuel bowl of the carburetor body and its outlet connected to a discharge tube in the venturi throat, fuel being supplied to the fuel bowl from the fuel pump after being regulated down to about 3.0 to 8.0 psi above the boost pressure.
Accordingly, it is a principal object of the invention to provide a boost fuel enricher for enriching the air/fuel mixture of an engine under boost from a turbocharger or supercharger in order to prevent damage to the engine from a lean air/fuel mixture.
It is another object of the invention is to provide a boost fuel enricher which enriches the air/fuel mixture in an engine under boost by a mechanically operated valve in order to provide and enriched air/fuel mixture dynamically for improved efficiency.
It is a further object of the invention to provide a boost fuel enricher which utilizes the venturi principle to meter the additional fuel required to enrich the air/fuel mixture in an engine under boost from a supercharger or turbocharger.
Still another object of the invention is to provide a boost fuel enricher that is capable of enriching a carbureted or fuel-injected internal combustion engine.
It is an object of the invention to provide improved elements and arrangements thereof for the purposes described which is inexpensive, dependable and fully effective in accomplishing its intended purposes.
These and other objects of the present invention will become readily apparent upon further review of the following specification and drawings.